In the fiber preparation field, webs or waddings of textile fibers (e.g. cotton fibers) of substantial width may constitute the feed material for certain of the fiber treating machines (e.g. carding machines). Such web-like bodies, referred to herein as laps, are generally continuous in length and they are fed on a generally continuous basis to the treating machines. In at least some such operations, it is desirable to ascertain thickness information concerning the laps as they are being fed. One manner of obtaining lap thickness information is to pass the lap through a gap between guide means and a movable sensor that is biased toward the guide means. As the thickness of the lap varies, the position of the sensor relative to the guide means varies and this provides a measure of the thickness and/or unevenness of the lap.
In known devices of this type, a single measuring roller extends over the entire maximum lap width and the position of this single measuring roller relative to a guide roller is taken as an indication of lap thickness. However, the travel of this measuring roller can only represent the highest particular lap thickness value that occurs locally at any zone across the entire length of the measuring roller. Moreover, a measuring roller of a length sufficient to extend across the entire lap width necessarily has a relatively high inertia, and systems utilizing such long measuring rollers are also inflexible because they cannot be matched to different lap widths.